1. Field of the Invention
The present invention relates to an apparatus and a method for CO2 recovery suitable for removing and recovering CO2 included in CO2-containing gas such as combustion waste gas, and more particularly relates to an apparatus and a method for CO2 recovery, in which CO2 included in CO2-containing gas is removed/recovered with improved energy efficiency.
2. Description of the Related Art
Recently, a greenhouse effect owing to CO2 has been pointed out as one of causes for global warming, and its measure has been internationally urgent in terms of preserving global environment. CO2 emission sources cover all activity fields of human beings who burn fossil fuels, and a requirement for its emission limitation is prone to further increase. Along with this, methods in which CO2 in combustion waste gas is removed and recovered by contacting the combustion waste gas from industrial facilities such as boilers and gas turbines with an amine based CO2 absorbing solution, and methods in which the recovered CO2 is stored without emitting in atmosphere have been actively studied for dynamogenesis facilities such as thermal power plants using the fossil fuels in a large amount. As a step of removing and recovering CO2 from the combustion waste gas using the CO2 absorbing solution as described above, those in which the combustion waste gas is contacted with the CO2 absorbing solution in an absorption tower, and the CO2 absorbing solution which has absorbed CO2 is heated in a regeneration tower to liberate CO2 as well as regenerate the CO2 absorbing solution, which is then reused by circulating it to the absorption tower again have been employed (e.g., see Japanese Patent Laid-Open No. 3-193116).
As shown in FIG. 7, the conventional CO2 recovery apparatus has a waste gas cooling device 1004 which cools waste gas 1002 containing CO2 discharged from the industrial facility such as a boiler and a gas turbine with cooling water 1003, a CO2 absorption tower 1006 in which the cooled waste gas 1002 containing CO2 is contacted with a CO2 absorbing solution 1005 which absorbs CO2 to remove CO2 from the waste gas 1002, and a regeneration tower 1008 in which CO2 is released from the CO2 absorbing solution (rich solution) 1007 which has absorbed CO2 to regenerate the CO2 absorbing solution. In this apparatus, the regenerated CO2 absorbing solution (lean solution) 1009 obtained by removing CO2 in the regeneration tower 1008 is reutilized as the CO2 absorbing solution in the absorption tower 1006.
In the method for recovering CO2 using this conventional CO2 recovery apparatus, first, pressure of the combustion waste gas 1002 containing CO2 from the industrial facilities such as boilers and gas turbines is increased by a waste gas air blower 1010, subsequently the waste gas is transferred to the waste gas cooling device 1004, cooled here with cooling water 1003, and then transferred to the CO2 absorption tower 1006.
In the CO2 absorption tower 1006, the waste gas 1002 is countercurrently contacted with the CO2 absorbing solution 1005 in which alkanolamine is a base, CO2 in the waste gas 1002 is absorbed into the CO2 absorbing solution 1005 by a chemical reaction (R—NH2+H2O+CO2→R—NH3HCO3), and the waste gas 1011 in which CO2 has been removed is discharged out of the system. The CO2 absorbing solution 1007 which has been absorbed CO2 is also referred to as a rich solution. The pressure of this rich solution 1007 is increased by a rich solvent pump 1012, and the rich solution is heated at a rich/lean solvents heat exchanger 1013 by the CO2 absorbing solution 1009 (lean solution) regenerated by removing CO2 in the regeneration tower 1008 described below and supplied to the regeneration tower 1008.
The rich solution 1007 infused inside the regeneration tower 1008 from an upper part of the regeneration tower 1008 releases the majority of CO2 by causing an exothermic reaction. The CO2 absorbing solution which has been released a part or majority of CO2 in the regeneration tower 1008 is referred to as a semi-lean solution. This semi-lean solution becomes the CO2 absorbing solution in which almost all CO2 has been removed until reaching a bottom of the regeneration tower 1008. This absorbing solution regenerated by removing almost all CO2 is referred to as a lean solution. This lean solution is heated with steam at a reboiler 1014. Meanwhile, the CO2 gas with water vapor released from the rich solution and the semi-lean solution in the tower is derived from a top part in the regeneration tower 1008, the water vapor is condensed by an overhead condenser 1016, water is separated by a separation drum 1017, and the CO2 gas 1018 is released out of the system and recovered. The water separated at the separation drum 1017 is supplied to the upper part of the regeneration tower 1008 by a condensed water circulation pump 1019. The regenerated CO2 absorbing solution (lean solution) 1009 is cooled with the rich solution 1007 at the rich/lean solvent heat exchanger 1013, subsequently its pressure is increased by a lean solvent pump 1020, and the lean solution is cooled at a lean solvent cooler 1021 and then supplied to the CO2 absorption tower 1006.
In FIG. 7, a numeral 1001a indicates a gas duct of the industrial facilities such as a boiler and a gas turbine and 1001b indicates a smokestack. The above CO2 recovery apparatus may be installed later for recovering CO2 from the waste gas source already disposed, or may be simultaneously annexed to the waste gas source newly disposed. An openable and closable cover is disposed at the smokestack 1001b , and set to close when the CO2 recovery apparatus is operated and open when the operation of the CO2 recovery apparatus is stopped even if a waste gas source is operated.
In the method for recovering CO2 from the CO2— containing gas such as combustion waste gas using the CO2 absorbing solution and the CO2 absorption step, it is necessary to reduce operation cost of the CO2 recovery apparatus itself as possible because the CO2 recovery apparatus is additionally installed to a combustion facility. In particular, in the above method for recovering CO2, it is important to develop a process which enables a reduction of consumed energy in the regeneration step because this regeneration step using the regeneration tower consumes much thermal energy.